Pointed heat-generating device for molds of injection molding machines

ABSTRACT

This invention relates to a pointed heat-generating device for molds of injection molding machines. It comprises a metal casing, a pointed projectile heat-generating means fixed with the metal casing, and a gate formed at the pointed heat-generating means and communicated to a cavity of the molds, characterized in that a heat-generating wire is penetrated wholly into a passage which is bored in a non-processed cylindrical material and an alloy portion is formed in an inert gas between an end of the heat-generating wire and the non-processed cylindrical material, thereby the alloy portion being formed as a pointed part of the heat-generating means by machining.

BACKGROUND OF THE INVENTION

The invention relates to a pointed heat-generating device for molds ofinjection molding machines.

The pointed heat-generating device is used widely for runnerlessinjection molding machines in order to fuse instantaneously syntheticresin existing at an injection gate communicating to a cavity of themolds, to open the injection gate and to inject the fused syntheticresin into the cavity.

A conventional pointed heat-generating device for molds of injectionmolding machines is disclosed in Japanese Pat. No. 902601, thecorresponding U.S. Pat. No. 3,800,027, U.K. Pat. No. 1,382,800, GermanPat. No. 2207001, French Pat. No. 72 05. 125, etc.

The above conventional heat-generating device is provided at its pointedend with such a heat-generating wire as a nichrome wire, wherein theheat-generating wire is generated intermittently in synchronization withan injection molding cycle. When carrying out an injection molding ofglass fiber containing synthetic resins in accordance with this process,the heat-generating wire is inclined to be worn. Further, there exists atwice-folded nichrome wire as a heat-generating member in order toreinforce its wear resistance. However, the heat-generating effect ofthe twice-folded nichrome wire is inferior to the aforementioned normalone.

For the purpose of eliminating the disadvantages of the prior art, theinventor of the present patent application invented a pointedheat-generating device shown in FIG. 1. It is disclosed in JapaneseUnexamined Utility Model Publication No. 56-55631 (corresponding toJapanese Utility Model application No. 54-136755) which was laid openfor public inspection on May 14, 1981.

In FIG. 1, there is mounted a coiled heat-generating means II within apointed section Ia of a heat-generating device I. Its heat generation isquite sufficient and its wear resistance is also improved. Nevertheless,the pointed section Ia is large at size and the heat-generating device Iitself is elongated. Accordingly, a heating response due to the increaseof heat capacity and a cooling response due to a switching operation arenot carried out suitably.

BRIEF SUMMARY OF THE INVENTION

It is an object of this invention to provide a pointed heat-generatingdevice for molds of injection molding machines, whereby particularlyprecise parts can be molded. The pointed heat-generating device inaccordance with the invention includes a metal casing, a pointedheat-generating means fixed with the metal casing and a gatecommunicated to a cavity of the molds, and is improved in that aheat-generating wire is penetrated wholly into a passage which is boredin a non-processed cylindrical material and an alloy portion is formedin an inert gas between an end of the heat-generating wire and thenon-processed cylindrical material, thereby the alloy portion beingformed as a pointed part of the heat-generating means by machining. Thepointed heat-generating means has an excellent wear resistance. Further,it is small-size and its heat capacity is lesser. Accordingly, a heatingand cooling process of synthetic resin at the gate can be carried outspeedily.

The novel features which are considered characteristic for the inventionare set forth in particular in the appended claims. The inventionitself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partially cutaway front view of a conventional pointedheat-generating device for molds of injection molding machines;

FIG. 2 is a partially cutaway transverse section view of an example of apointed heat-generating device for molds of injection molding machinesaccording to this invention;

FIG. 3 is a partially cutaway longitudinal section view of the device inFIG. 2;

FIG. 4 is a right side view of the device in FIG. 2;

FIG. 5 is a view of a heat-generating wire inserted in a passage boredin a non-processed cylindrical material;

FIG. 6 is an enlarged section view of an alloy portion formed as apointed part of the device according to this invention;

FIG. 7 is a partially cutaway transverse section view of other exampleof the pointed heat-generating device according to this invention;

FIG. 8 is a partially cutaway longitudinal section view of the device inFIG. 7;

FIG. 9 is a right side view of the device in FIG. 8; and

FIG. 10 is an enlarged section view of the pointed heat-generating meansin the above example.

PREFERRED EMBODIMENTS OF THE INVENTION

A first example of this invention will be described with reference toFIGS. 2 to 6.

A heat-genearing device A comprises a body 1, a metal casing 2 having abase 2a, and a pointed heat-generating means 3. The device A is of aprojectile shape as a whole. The metal casing 2 is made of such aheat-proof metal as e.g. stainless steel. It has a cylindrical innerwall 4. The heat-generating means 3 is pointed and nearly conical. It isprovided, at its rear end, with a cylindrical fitting portion 5 forreceiving and fitting the metal casing 2. A passage 6 extends in anaxial direction of the heat-generating means 3. A heat-generating wire 7such as e.g. a nichrome wire is penetrated wholly into the passage 6until its end reaches a pointed end of the heat generating means 3. Anend portion of the heat-generating means 3 forms an alloy portion X ofwear resistance which is nearly equivalent to that of a material of theheat-generating means 3.

How to make the alloy portion X will now be described. As shown in adot-and-dash line of FIG. 5 there is a non-processed cylindricalmaterial 3a.

First of all, the passage 6 is bored in the non-processed cylindricalmaterial 3a, and the heat-generating wire 7 is penetrated into thepassage 6. An end of the non-processed cylindrical material 3a and anend of the heat-generating wire 7 are fused locally and united to eachother in such an inert gas as argon and converted into an integral part,that is the alloy portion X by means of arcing.

Thus, the alloy portion X has the nearly same wear resistant property asthe heat-generating means 3. By cutting and processing the cylindricalmaterial 3a, there is formed the pointed heat-generating means 3 havingthe alloy portion X as a peak. As a result, the heat-generating means 3becomes small-size and its heat capacity becomes lesser.

The heat-generating wire 7 is extended to the cylindrical inner wall 4and covered by e.g. an alumina insulating tube 8 which is inserted intothe enlarged passage 6. Since heat conductivity of the heat-generatingwire 7 is secured sufficiently, the pointed part of the heat-generatingportion 3 maintains a sufficient heating effect by way of theheat-generating wire 7. Another end of the wire 7 is connected to a leadwire 9 located at an end of the alumina tube 8 and connected to anoutside circuit by way of a guiding opening 10 provided at a rear end ofthe metal casing 2.

On the other hand, an exterior of the alumina tube 8 is coiled by asecond heat-generating wire 11. One end of the second heat-generatingwire 11 is connected to the fitting portion 5, while the other endthereof is connected to a lead wire 12 by way of the guiding opening 10.

Further, the second heat-generating wire 11 is electrically insulated bya second alumina tube 13 fitted on the inner wall 4, but it maintains asufficient heat conductivity. The first and second heat-generating wires7 and 11 respectively are connected to the pointed heat-generating means3 and the metal casing 2. A rear end of the metal casing 2 is providedwith a terminal 14 which is connected to two lead wires 15a, 15b. Theyare connected to an outside circuit through the guiding opening 10.

Numeral 16 is a pair of supply paths for supplying synthetic resin whichare mounted in parallel with each other to an axial direction of themetal casing 2. Numeral 17 is synthetic resin. Numeral 18 is aninjection gate. Numeral 19 is a cavity. Numeral 20 is a temperaturesenser. Numeral 21 is a lead wire for the temperature senser 21. Numeral22 is an insulating material such as magnesium hydroxide which is filledwithin the metal casing.

A function of the pointed heat-generating device according to the firstexample will be described. A joule heat of the heat-generating wire 11which is generated by energizing is conducted to the insulating tube 13and the metal casing 2 one after another. As a result, the syntheticresin covering the metal casing 2 as well as the pointed heat-generatingmeans 3, and the synthetic resin supplied in the supply paths 16 are allfused. As described previously, since the pointed part of theheat-generating means 3 and the heat-generating wire 7 form an integralstructure, that is the alloy portion X, it has excellent rigidity andwear resistance. Accordingly, the alloy portion X is formed small atsize and its heat capacity becomes lesser.

Further, the pointed heat-generating device of the invention can be usedeffectively for such a narrowed gate 18. By turning off a power sourceto the heat-generating wire 7, the fused synthetic resin is cooledimmediately and solidified. Conversely, by turning on the power source,it is heated immediately and fused. Due to an ON-OFF switching of thepower source, the synthetic resin 17 at the gate 18 is fused orsolidified, in response to which the gate 18 is opened or closed. Thus,a very accurate injection molding is feasible.

A second example of this invention will now be described with referenceto FIGS. 7 to 10. When the numerals in the second example are the sameones as the first example, their description will be omitted.

The metal casing 2 is provided with a stage 23 adjacent the base 2a. Thestage 23 is provided with a pair of slit grooves 24 at its upper sideand lower side in order to ease a cooling effect of a mold coolingwater, while the winding number of the second heat-generating wire 11 isincreased in the proximity of the stage 23 for the same purpose. Thus,by raising locally the temperature of heat generation, it is possible toease the cooling effect of the cooling water.

Numeral 25 is a protective tube for protecting the lead wires, theprotective tube 25 being fixed with walls of the guiding opening 10. Anend of the protective tube 25 is fixed with a coil spring 26.

The alloy portion X shown in FIG. 10 is basically formed in the samemanner as shown in FIG. 5. In the second example a shorter insulatingtube 8 is used and an oxide layer 7a coats an exterior of the pointedpart of the heat-generating wire 7 in order to enhance insulationthereof furthermore.

Further, by mounting the senser 20 at an end of the heat-generatingmeans 3, it is possible to control the temperature in the proximity ofthe heat-generating means 3. In this example, only four lead wires areused.

According to one aspect of this invention, the alloy portion formed atthe pointed part of the heat-generating means has an excellent wearresistance for flow of the fused synthetic resin, particularly a fusedfiber-containing synthetic resin. And durability of the heat-generatingmeans is extended remarkably. Further, since the alloy portion is formedat a small size by accurate cutting and processing, it is very suitablefor molding precise plastic products. Further, since the heat capacityof the heat-generating means becomes lesser, the synthetic resin at theinjection gate may be heated or cooled speedily.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in apointed heat-generating device for molds of injection molding machines,it is not intended to be limited to the details shown, since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. An improved pointed heat-generatingdevice for molds of injection molding machines comprising a metalcasing, a pointed projectile heat-generating means fixed with an end ofthe metal casing, a gate formed at the pointed heat-generating means andcommunicated to a cavity of the molds, and a synthetic resin materialbeing fused or cooled or solidified at the gate by an electric ON-OFFswitching of the pointed heat-generating means, thereby the gate beingopened or closed intermittently, wherein the improvement comprises analloy portion formed by fusing of an end of a heat-generating wirepenetrated wholly into a passage which is bored in a non-processedcylindrical material, with the non-processed cylindrical material, andthereby the alloy portion can be shaped as a pointed part of the heatgenerating means by machining.
 2. A pointed heat-generating device formolds of injection molding machines as claimed in claim 1, in which theheat-generating wire integrally united to the alloy portion passesthrough the inside of the metal casing and is connected to a lead wire,thereby the pointed heat-generating means can to be energized by a powersource connected to the lead wire.
 3. A pointed heat-generating devicefor molds of injection molding machines as claimed in claim 1, in whichthe heat-generating wire connected to the pointed heat-generating meansis, on its outer circumference, wound by a second heat-generating wirein order to heat and fuse synthetic resin upon a surface of the metalcasing.
 4. A pointed heat-generating device for molds of injectionmolding machines as claimed in claim 1, in which the metal casing isprovided with a pair of supply paths for supplying synthetic resin, thepair of supply paths being mounted in parallel with each other to anaxial direction of the metal casing.
 5. A pointed heat-generating devicefor molds of injection molding machines as claimed in claim 1, in whichthe metal casing is provided with a stage adjacent a base of the metalcasing, the stage being provided with a pair of slit grooves at itsupper and lower side in order to ease a cooling effect of a mold coolingwater, while the winding number of the second heat-generating wire isincreased in the proximity of the stage for the same purpose.